1. Field of the Invention
The invention relates to a control system for a hybrid vehicle that uses a motor, which is used to control the rotation speed of an engine, as a driving force source that outputs driving force for propelling the hybrid vehicle.
2. Description of Related Art
A so-called two-motor hybrid vehicle is described in Japanese Patent Application Publication No. 8-295140 (JP 8-295140A). The hybrid vehicle includes a power split mechanism formed of a planetary gear mechanism. Torque output from an engine is input to a carrier of the planetary gear mechanism, and a first motor having a power generating function is coupled to a sun gear of the planetary gear mechanism. A ring gear is an output element of the planetary gear mechanism. The ring gear is coupled to a differential via a counter gear unit that constitutes a speed reduction mechanism. A second motor is coupled to the counter gear unit. Electric motor generated by the first motor is allowed to be supplied to the second motor. In addition, a brake that stops rotation of an input shaft coupled to the carrier is provided. In a state where the carrier is fixed by engaging the brake, the power split mechanism functions as a speed reduction mechanism, and is able to amplify torque output from the first motor and output the amplified torque from the ring gear.
International Application Publication No. 2011/114785 describes a system having a similar configuration to that of the hybrid drive system described in JP 8-295140 A. In the drive system of this type, for example, if a vehicle is towed in a state where an engine is stopped, because a carrier is stopped, there is a possibility that it becomes insufficient to supply lubricating oil to pinion gears, pinion pins, and the like. In the system described in International Application Publication No. 2011/114785, a receiver that receives lubricating oil falling from a liquid pool portion provided above a planetary gear mechanism and then guides the received lubricating oil to the pinion pins is provided.
In the hybrid vehicle described in JP 8-295140A, when the engine is stopped and rotation of the carrier is stopped by the brake, the power split mechanism serves as a speed reducer. When the first motor is caused to function as a motor in this state, torque of the first motor is amplified and output from the ring gear, so it is possible to propel the hybrid vehicle. In this case, because the carrier does not dip lubricating oil, there arises a situation that it is not possible to sufficiently supply lubricating oil to the pinion gears, the pinion pins, and the like, as described in International Application Publication No. 2011/114785.
The system described in International Application Publication No. 2011/114785 is configured to guide lubricating oil falling from the liquid pool portion provided above the planetary gear mechanism to the pinion pins or the pinion gears. Therefore, when lubricating oil is sufficiently pooled in the liquid pool portion, it is possible to supply lubricating oil to the pinion pins, the pinion gears, and the like. However, for example, when lubricating oil in the liquid pool portion runs dry or does not sufficiently fall because of high-viscosity lubricating oil, there is a possibility of insufficient lubrication of the pinion pins, the pinion gears, and the like. Because it is required to provide the above-described liquid pool portion, it is required to significantly modify an existing system, and there is a possibility that the size of the overall configuration of the hybrid system increases.